Octostruma balzani is a widespread Central and South American species that is common in many localities. It occurs in a variety of forested habitats: wet to seasonal dry, second growth to mature, lowland to montane. It usually occurs from sea level to the lower edges of cloud forests, typically around 1400 m. The highest elevation record is 1650 m in Nuevo León, Mexico. Almost all collections are from Berlese and Winkler samples of sifted litter and rotten wood from the forest floor. In quantitative 1 m2 litter plot samples, within-sample abundance is tens of workers or fewer, but the species can occur in nearly every sample, suggesting a high density of small colonies. Dealate queens and intercaste workers often occur together with workers in litter samples. (Longino 2013)

Identification

Keys including this Species

Distribution

Longino 1999 for what is called the balzani complex - Tropical Mexico south through Central and South America at low and moderate elevations to the Bolivian Andes and to Parana and Sao Paulo states in southeastern Brazil; Trinidad, Dominica, and probably other islands of the Lesser Antilles (Brown and Kempf 1960).

Biology

Longino (2013) - Brown and Kempf (1960) summarized the biology of basicerotines as follows: The basicerotines all come from tropical or subtropical areas, and predominantly from mesic habitats, particularly rain forest, where they live primarily in the upper layers of the soil and in the soil cover, including large and small pieces of rotten wood. They are fairly common in soil cover berlesates. Nests have been found in snail shells, and in the peaty masses gathered about epiphytic ferns above the ground level. So far as is known, colonies are small, consisting of one or more dealate—or rarely ergatoid—females, and a few workers. Judging from the structure of the workers and females, one would suppose that they were predaceous on small arthropods...

Besides this summary, the behavior of three basicerotine species has been studied. Wilson (1956) observed a small captive colony of Eurhopalothrix biroi, a New Guinea species. Workers moved slowly and captured a variety of small, soft-bodied prey, including spiders, symphylans, entomobryid Collembola, campodeids, and hemipteran nymphs. Wilson and Brown (1984) observed a captive colony of Eurhopalothrix heliscata, a species from Singapore. The colony contained over 400 workers, multiple alate and dealate queens, several adult males, and brood. Foraging workers acted "rather like miniature ferrets," readily wedging themselves into small crevices. They foraged solitarily, attacking a variety of prey but mostly termites. They used their sharply-toothed mandibles to abruptly snap onto appendages of prey, maintaining purchase and slowly reaching around with the gaster to sting the prey. The strongly sclerotized labrum was also employed to press against the clamped appendage. The behavioral repertoire was limited. There did not appear to be trophallaxis, as workers and larvae fed directly from prey in the brood chambers. Nor did there appear to be any form of alarm communication. While there was generally an increase in the number of foragers when clusters of prey were presented, there was no evidence of any pheromone-based recruitment. Workers were non-aggressive and responded to disturbance by tucking the appendages and becoming immobile, often for minutes at a time. Wilson and Hölldobler (1986) studied captive colonies of Basiceros manni from Costa Rica and observed behavior not substantially different from E. heliscata. Foraging workers of many basicerotines are often encrusted with a firmly bonded layer of soil, which is thought to function as camouflage, enhancing crypsis (Hölldobler & Wilson, 1986).

Knowledge of the basic natural history of these ants has hardly progressed since the observations of Wilson, Brown, and Hölldobler. More specimens are now available for examination due to quantitative litter sampling, enhancing knowledge of basicerotine diversity and distribution, but discovering nests remains exceedingly difficult. Quantitative samples of 1 m2 litter plots reveals that small basicerotines can be very frequent, occurring in over 50% of samples in some cases, but never in large numbers. Individual samples usually contain fewer than ten workers, and workers are often accompanied by dealate queens. These results suggest that colonies, at least among New World species, are usually small, with tens of workers.

Less than half of the species of Octostruma have their queens described. Ergatoid queens are known from some species. Males are known from collections for some species but none have been described. The mating biology of these ants and how common ergatoid queens are across the genus and within colonies is not known.

Castes

Worker

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Head view

Side view

Top view

Specimen labels

Queen

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Head view

Side view

Top view

Specimen labels

Nomenclature

The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.

The general form of the head and alitrunk and petiole varies within limits individually and among different nest series. Occiput convex and anterior part of cephalic dorsum flat or shallowly concave; the meeting of these two surfaces often produces a feebly indicated, blunt ridge or rise crossing the head in an arc and corresponding to the carina found in rugifera and rugiferoides. Lateral occipital (postocular) angles obtuse to obsolete.

Mandibles of moderate length, their upper surfaces feebly convex, external margins weakly convex in outline; masticatory border and teeth very slightly depressed; usually 7 larger teeth, with 2-3 minute intercalary denticles. Basal tooth most commonly broad and bluntly rounded or subtruncate, filling or nearly filling the space between mandibles and clypeus at full closure. In occasional specimens from the northern part of the range (thus away from the range of the sibling O. stenognatha), the basal tooth is variably narrowed to a blunt point, but never to the extent of stenognatha. The compound eyes vary in size from small to very small, apparently allometrically corresponding to degree of gynecoidy.

Alitrunk often more convex above in outline; metanotal groove varying from reasonably distinct, or more feeble, to virtually obsolete on the dorsum. Propodeal teeth also somewhat variable in size and shape. Petiolar node varying to a much more rounded summit profile; as seen from above, node proper about twice as long as broad in most samples, rectangular. Postpetiole subreniform, broader than petiole (but not twice as wide) and about half or a little more as wide as the first gastric segment.

The stubby erect clavate hairs vary considerably in number present; the pattern is a common one, allowing for hairs broken off. Additional pairs of hairs added on head, alitrunk, postpetiole and gastric dorsum commonly accompany increase in size, and apparently represent a gynecoidal tendency. The alitrunk may have no erect hairs, but often 1, 2, or even as many as 3 pairs are present. On the dorsum of the first gastric segment, the number of hairs is usually between 6 and 12, but may reach as high as 20 or more, mostly concentrated on the posterior 2/3 of the segment in rows of 4 or 6. Ground hairs are generally appressed or reclinate and inconspicuous, but in some samples they are easily seen, though appressed, on clypeus, anterior part of head or gastric dorsum, or all three places. Sculpture densely and regularly punctulate. prevailingly opaque. Color varying shades of reddish-brown.